Flux-cored wires for use in welding initial layers of pipelines have been conventionally required to have excellent welding workability and further excellent mechanical properties (tensile strength and absorbed energy at a low temperature) of weld metal in the as-welded (AW) condition: so-called AW performance.
Patent Document 1 proposes a flux-cored wire for gas-shielded arc welding with excellent welding workability that can produce good penetration beads in welding an initial layer of a pipeline. The wire composition is characterized by filling 8 to 20% by mass of a flux into a steel outer sheath made of C: 0.08% or less by mass, the flux containing: alkali metal: 0.1 to 5% by mass, a ratio of (Na/K): 1 to 50%, C: 0.3 to 2.5% by mass, metal powder: 80% or more by mass, and a slag former.
Patent Document 2 proposes a flux-cored wire for Ar—CO2 mixed gas-shielded arc welding with excellent AW performance. The wire structure is characterized by including a flux filled into a steel outer sheath, the flux containing 97% or more by mass of metal powder, the metal powder containing 4.0 to 15.5% by mass of iron powder, relative to the total mass of the wire, the iron powder containing 0.25% or less by mass of oxygen, furthermore, the wire components of the wire structure containing, in percent by mass relative to the total mass of the wire: C: 0.03 to 0.12%, Si: 0.5 to 1.2%, Mn: 1.5 to 3.5%, S: 0.005 to 0.05%, and one, or two or more kinds of an alkali metal oxide, an alkali metal fluoride, and a metal oxide in total: 0.35% or less, with the balance being Fe and inevitable impurities.